This invention relates to the upgrading of hydrocarbon residues to obtain valuable products therefrom. More specifically the invention relates to a severe visbreaking process.
It is important to find improved methods of processing petroleum residua because the quantity of high quality petroleum stock is dwindling. More of the higher value petroleum products must be obtained from, the whole crude and in particular from the resid.
Visbreaking is a mild cracking operation used to reduce the viscosity of heavy residue. The heavy residues are sometimes blended with valuable light oil, or cutter stocks, to produce oils of acceptable viscosity. By use of visbreakers, the viscosity of the heavy residue is reduced so as to lower the requirement of the cutter stock.
Sometimes visbreakers are also used to generate more gas oils for catalytic cracking and naphtha for reforming to increase the gasoline yield in the overall refining operation. To achieve these goals, the visbreaker has to be operated at high enough severity to generate sufficient .quantity of lighter products.
The economic and environmental factors relating to upgrading of petroleum residual oils and other heavy hydrocarbon feedstocks have encouraged efforts to provide improved processing technology, as exemplified by the disclosures of various U.S. patents which include U.S. Pat. Nos. 2,160,814; 2,358,573; 2,695,264; 2,733,192; 3,065,165; 3,696,027; 3,730,879; 3,775,303; 3,870,621; 3,876,530; 3,882,049; 3,897,329; 3,905,893; 3,901,792; 3,964,995; 3,985,643; 4,016,067; 4,054,504; 4,379,747; and the like.
U.S. Pat. No. 4,334,976 discloses a process for upgrading residual oil by heating an admixture of heavy hydrocarbon oil and particulate coal under visbreaking conditions. The heat treatment may be conducted in the presence of hydrogen to increase demetallation of the feedstock, to suppress formation of coke and to increase liquefication of the particulate coal phase. In U.S. Pat. No. 4,544,479 the visbreaker may operate with some hydrogen addition but may operate with no hydrogen addition.
U.S. Pat. No. 4,504,377 discloses a two-stage visbreaking process. The second stage visbreaking is conducted under relatively high severity in contact with a fluidized bed of particulate solids.
U.S. Pat. No. 4,615,791 discloses a visbreaking process may be carried out at high severities in the presence of an aromatic hydrogen donor solvent. There is no disclosure of a visbroken product
To improve process economics, the visbreaking should be operated at high severities. However, the operable severity is limited by the formation of insolubles or "coke" which leads to furnace coil fouling and product instability.
Accordingly, it is an object of the present invention to provide a process to maximize visbreaking severity in order to reduce the cutter stock requirement. It is a further object of this invention to provide a process to maximize visbreaking severity to increase distillate yield. It is another objective of this invention to produce stable fuel oil for sale and high quality stock for further processing, such as catalytic cracking. Other objects and advantages of the present invention will become apparent from the accompanying description and illustrated data.